Seal housing with helical element

ABSTRACT

A cavity in the housing, which confines the seal therewithin, has an annular wall surface which is modified to direct liquid from the cavity towards the impeller. In one embodiment, the wall surface has a helical land formed therein. In another embodiment, a helical-land forming insert is set within the cavity and in engagement with the wall surface.

BACKGROUND OF THE INVENTION

This invention pertains to seal housings, for use in rotary machinessuch as pumps or liquid mixers, and the like, and in particular to sealhousings for mechanical face seals arranged between the hydrauliccomponents of the machine and the driving motor therefor, as is typicalin pumps of the centrifugal type.

A conventional centrifugal pump comprises a driving unit, such as anelectric motor, and a pump housing connected via a driving shaft. Inorder to prevent the pumped medium from entering the electric motor viathe shaft, and cause damage, some sort of seal is arranged between thepump housing and the motor. A typical seal is the so-called mechanicalface seal which consists of a rotary seal ring and a stationary sealring which are pressed towards each other by a biasing force.

Seals of the aforesaid type are very effective, providing that the twoseal surfaces are even and undamaged. In order to effect a perfectsealing, there is often used an arrangement consisting of two mechanicalseals with an intermediate, intervening oil chamber. In this way, one ofthe seals will always be lubricated and cooled by clean oil, and therisk of damage is greatly reduced. Of the two seals, the one which facesthe pump housing, here called the lower seal, will always be exposed tobe pumped medium, and damage can result if the pumped medium containsabrasive particulate. The latter is a circumstance which is common inmines and certain other industrial areas.

The lower seal is normally mounted in a cavity which has a cylindricalor conical form. If conical, the portion with the greater diameterconfronts the pump housing. Conical form bas manufacturing reasons, butit is also used on the theory that particles, which enter the cavity,will be thrown out again by centrifugal force. In fact, however,pollutants are concentrated at the inner part of the cavity where theymay damage the seal surfaces as well as the cavity wall. This phenomenonalso occurs in seal housings where the cavity has a cylindrical-formedshape.

Concentration of pollutants proceeds from the fact that rotation of thepumped medium generates secondary flows of such a nature that rotatingsurfaces induce a radially outwards-directed flow, while stationarysurfaces induce a radially inwards-directed flow. Particles within theseal housing will be thrown outwards to the cylindrical or conical wallsurface by centrifugal force, the boundary layer flow along the wallsurface then directing the particles within the housing toward the seal.

The particles are not transported back to the pump impeller, at theoutlet of the seal housing, as the backwards directed flow is weakerthan the inwards-directed flow, and because of the fact that thecentrifugal force again throws the particles towards theinwards-directed boundary layer flow. The result is that particles whichonce have entered the seal housing will never leave it, but areconcentrated in the inner part of the housing where they cause wear ofthe housing and the seal.

In order to diminish the risk of wear of the seal ring surfaces and theseal housing, there have been prior art attempts to change the flowpattern in the seal area. An example thereof is shown in U.S. Pat. No.4,872,690, where an additional means is mounted which turns the flow andthus sometimes solves the problem.

According to the instant invention, the problem of changing the flowpattern in the seal housing of a centrifugal pump is solved by modifyingthe wall of the seal housing cavity.

SUMMARY OF THE INVENTION

It is an object of this invention to set forth an improved seal housingfor a rotary machine, such as a pump or mixer for liquids, whichcomprises a driving motor, a hydraulic part with a rotary impellerconnected to the motor via a shaft, and a mechanical face seal arrangedwithin a cavity, in said seal housing, which cavity (a) has an annularwall surface, and (b) openly confronts the impeller, wherein theimprovement comprises means on said annular wall surface defining ahelical land, said means being cooperative in response to rotation ofsaid shaft for directing liquid from said cavity toward said impeller.

Another object of this invention is to disclose a shaft seal housing,for a rotary machine which has a fluid-working impeller, comprising abody, centrally-bored for journalling an impeller-driving shaft therein;wherein said body has a cavity, formed therein, which openly confrontssaid impeller; said cavity has an annular wall surface; and said wallsurface has means, cooperative in response to rotation of said shaft,for directing liquid from said cavity toward said impeller.

Further objects of this invention, as well as the novel featuresthereof, will become apparent by reference to the following description,taken in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an axially-taken cross-sectional view through a prior artcentrifugal pump having a typical seal housing therein;

FIG. 2 depicts a prior art seal housing, confronting an impeller, inwhich the common flow patterns are shown;

FIG. 3 is an illustration, like that of FIG. 2, in which, however, anembodiment of the invention is shown; and

FIG. 4 is a view like that of FIGS. 2 and 3, albeit of an alternativeembodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, the pump has an electric motor driving unit 1, a hydraulicunit 2, with a pump impeller 3 connected to the driving unit 1 by ashaft 4. The seal housing 5 has a cavity 6 formed therein whichconfronts the impeller 3. Within the cavity 6, and about the shaft 4, isa mechanical face seal 7, the latter comprising a rotary sealing element8, a stationary sealing element 9, and a compression spring 10 urgingthe two elements into engagement.

The aforesaid seal housing 5, cavity 6, seal 7 and shaft 4 are shown ingreater detail and in enlargement in FIG. 2. The captive flows ofliquid, within the cavity 6, are shown in FIG. 2 by the arrows. Theliquid flows in loops in the cavity 6 which means that abrasiveparticulate stays within the cavity. Consequently, damaging wearsubsequently occurs.

FIG. 3 depicts an embodiment of the invention. Here the cavity 6a has ahelical land 11 formed in the annular wall surface 12 thereof. Now,particles that have entered the cavity 6a are transported by theboundary layer flows towards the bottom of the cavity 6a. By the designof the land 11, such migration of the particles is prevented bycentrifugal force. Instead, the particle will be caught by the land 11and follow it, helically, out of the cavity 6a towards the impeller 3.

The land 11 may have various inclinations and profiles, and a pluralityof helical lands may be used, such being alternative embodiments of theinvention.

In FIG. 4 an alternative embodiment of the invention is shown where, inlieu of a land 11 being formed in the annular wall surface 12 of thecavity 6, a helical insert 13 is set within the cavity 6 and inengagement with the wall surface 12.

While I have described my invention in connection with specificembodiments thereof it is to be clearly understood that this is doneonly by way of example and not as a limitation to the scope of theinvention, as set forth in the objects thereof and in the appendedclaims.

I claim:
 1. An improved housing for a pump which comprises a drivingmotor (1), a hydraulic part (2) with a rotary impeller (3) connected tothe motor (1) by a shaft (4) and a seal housing (5) located between themotor (1) and the hydraulic part (2), the housing (5) contains a cavity(6) adjacent the impeller (3), within said cavity (6) and around theshaft (4) is a mechanical seal having a stationary sealing element (9),a rotary. .,.!. sealing element (8), and a compression spring (10)urging the elements (8), (9) into engagement, wherein the improvementcomprises:said cavity (6) having a conical shape and an . .annual.!..Iadd.annular .Iaddend.wall surface (12), and a . .single.!. helicalelement .Iadd.(11), .Iaddend.(13) . .is positioned in said cavity (6).!.spaced from said mechanical seal and . .engaging.!. .Iadd.extending.Iaddend.from top to bottom of said wall surface (12), whereby a liquidpresent near said wall surface (12) is directed toward said impeller (3)due to rotary motion that the liquid obtains when the shaft (4),.Iadd.rotary .Iaddend.element (8) and spring (10) rotate. .Iadd.
 2. Theimproved housing for a pump according to claim 1, wherein said helicalelement is a helical land (11) formed in said annular wall surface (12)of said cavity (6). .Iaddend..Iadd.3. The improved housing for a pumpaccording to claim 1, wherein said helical element is a helical insert(13) positioned in said cavity, said helical insert engaging saidannular wall surface (12) from said top to said bottom thereof..Iaddend.